Optical waveguide module

Abstract: The present invention is directed to an optical waveguide module which is arranged to be free from a breakage of a coupling part of an optical waveguide and optical fibers which are housed in a housing and deviation of an optical axis at this coupling part even though a tensile force is applied to optical fibers. A waveguide board (14) having an optical waveguide (13) is housed in a housing (10) and an optical connector (15) to which bare optical fibers (16) are connected is bonded to an end face of the waveguide board to form a first holding part (17). An optical fiber conductor (11) and an optical fiber tape (12) are introduced into the housing (10) through a side wall (18) of the housing, and the covering parts of the optical fiber conductor and an optical fiber tape are bonded to the side wall of the housing with a bonding agent to form a second holding part (21). The bonding strength of the second holding part (21) ia determined to be larger than the bonding strength of the first holding part (17).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical waveguide module for use in optical fibers communications network and the like. Related Background Art An optical waveguide module is generally formed with a module unit which is provided to connect an end face of an optical waveguide and end faces of optical fibers and housed in a housing sealed with nitrogen gas or the like. In this optical waveguide module, a covering member for the optical fibers is fixed to a part of the housing to stationarily stabilize the module unit. Various methods for increasing a strength of a coupling part of the end faces of the optical waveguide and the optical fibers have been studied. As regards the coupling part of the optical waveguide and the optical fibers, there have been many restrictions such as, for example, necessities of centering of the optical axis and use of synthetic resin material having a refractive index of which matches those of the optical waveguide and the optical fibers. The optical waveguide and the optical fibers may be connected in an arrangement as shown in Fig. 1 to ensure complete connection. A block 3 is mounted on an upper surface of a waveguide board 2 on which an optical waveguide 1 is formed, a connector 5 connected to the end faces of the optical fibers 4 is positioned to abut against the end face of the waveguide board 2 and the end face of the block 3 and fixed with a bonding agent. In the arrangement shown in Fig. 1, the block 3 is mounted on the waveguide board 2 and the strength of the coupling part of the waveguide board 2 and the optical fibers 4 is increased by increasing a contact area with the connector 5. However, this method requires a work such as alignment with the block 3 for which attentions should be exercised. EP 0 456 026 discloses a device having fibres coupled to end faces of integrated waveguides. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide module which is housed in a housing and adapted so that, even when a tensile force acts on the optical fibers and this tensile force is conducted to the coupling part of the optical waveguide and the optical fibers, the deviation of the optical axis and the destruction of the coupling part may be prevented. To realize the above-described object, it is an object of the present invention to provide an optical waveguide module according to claims 1 and 5. Since the bonding strength of the first fixing part is provided to be larger than that of the second fixing part, even when an external force acts on the optical fibers so as to pull the optical fibers from the housing, the external force is received by the first holding part and the coupling part of the optical waveguide and the optical fibers is free from an excessive tensile force so that the first holding part becomes strong against a mechanical tensile force. The strength of the first holding part is increased by applying the bonding agent both to a bare optical fiber part at the ends of the optical fibers and to a covered optical fiber part. If only the covered optical fiber part is bonded in a case that the bare optical fibers may be separated from a surrounding covering member inside the covered optical fiber part, the tensile force may be directly applied to the coupling part of the bare optical fiber part and the optical waveguide. Such trouble is eliminated by bonding both the bare optical fiber part and the covered optical fiber part. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art form this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a coupling arrangement of an optical waveguide and an optical fiber according to the related art background art; Fig. 2 is a perspective view of an optical module Fig. 3 is a partly omitted plan view of the optical module according to the first embodiment; Fig. 4 is a partly omitted plan view of the optical module according to the second embodiment; Fig. 5 is a partly omitted plan view of the optical module according to the third embodiment; Fig. 6 is a perspective view of a connector shown in Fig. 5; Fig. 7 is a disassembled perspective view of the optical module according to the forth embodiment; Fig. 8 is a vertical sectional view of a completed optical module according to the forth embodiment; Fig. 9 is a disassembled perspective view of the optical module according to the fifth embodiment; and Fig. 10 is a perspective view of the optical module according to the fifth embodiment shortly before the cover is fixed. Referring to Fig. 2, there is shown an interior of a housing 10 of an optical waveguide module. A single-core optical fiber 11, that is, one bare optical fiber covered with a synthetic resin member, and a tape-like optical fiber cable 12 in which 8-optical fibers, that is, eight bare optical fibers are covered with the synthetic resin member integrally are coupled to an optical waveguide 13 which forms a 1 × 8 coupler through a connector 15 whereby a module body is formed. Specifically, the optical waveguide 13 is formed as a 1 × 8 coupler by depositing a quartz glass layer on a waveguide substrate 14 made of a chip type monocrystalline silicon material by a flame deposition method. A connector 15 is fixed to both ends of the waveguide substrate 14 with a bonding agent and this fixing part of the waveguide substrate 14 and the connector 15 is formed as a second fixing part 17 which optically couples the optical waveguide 13 and the bare optical fiber 16. An entrance side of optical signals to the optical waveguide 14 is coupled to the single optical fiber 11 through the connector 15 at the left side in Fig. 2 after alignment of optical axes. An exit side of optical signals from the optical waveguide 14 is coupled to an tape-like optical fiber cable 12 through the connector 15 at the right side in Fig. 2 after alignment of optical axes. All connectors 15 respectively have a V groove formed on the silicon chip and the bare optical fibers 16 are inserted into this V groove to form the optical waveguide and the end surface of the connector is fixed to the end surface of the waveguide substrate 14 with a bonding agent. The above-described bonding agent for fixing the waveguide substrate 14 and the connector 15 is limited to a type which is transparent to a signal light and has a refractive index adjusted to those of the waveguide 13 and the bare optical fiber 16. End surfaces of both side walls 18 of the housing 10 are slightly concaved as concavities 19 into which the single-optical fiber 11 and a tape-like multi-optical fiber cable 12 are placed. The optical fiber 11 and the tape-like optical fiber cable 12 are fixed to each concavity 19 to form a first holding part 21 by pouring a bonding agent into the concavity 19 along the optical fiber 11 and the tape-like optical fiber cable 12. For coupling the connector 15 which holds the bare optical fiber 16 and the waveguide board 14, it is necessary to use an optical bonding agent which is limited in types available for this purpose. Generally, however, this type of bonding agent only provides a weak bonding strength. A bonding area between the waveguide board 14 and the connector 15 is generally small as approximately 1 mm × 5 mm and the fixing strength by bonding in this case is approximately 0.5 kgf, which cannot withstand a tensile force to be actually applied to the optical fibers. (Therefore, the bonding area with the connector part has been increased by using a reinforcing block 3 as shown in Fig. 1.) In a tension test of the optical fibers in the optical waveguide module, the evaluation is generally made in reference to a strength of 1 kgf. In handling the optical waveguide module in cases other than the tension tests, a tensile force of approximately 1 kgf may be readily applied to the optical fibers. Accordingly, a larger force than the specified strength is applied to the coupling part of the optical waveguide board 14 and the connector 15 and a breakage or an axial deviation may be caused at this coupling part. Therefore, a type of bonding agent and a length of a bonding part are determined for fixing so that the strength of the first holding part 21 with which the optical fiber 11 and the tape-like optical fiber cable 12 in the housing 10 are fixed each other is larger than the strength of the second holding part 17 with which the waveguide board 14 and the connector 15 are fixed each other. In this case, it is preferable to fix them each other so that the fixing strength in bonding of the optical fiber 11 and the tape-like optical fiber cable 12 to the housing 10 at the first fixing part 21 is 1 kgf or over. Both the single optical fiber and the tape-like multi optical fiber cable respectively have bare optical fibers made of quartz glass at its center and outside of them are covered with a synthetic resin material so that the synthetic resin material is functioned as a covering layer. The covering layer is generally multi-layered and the internal layer is made of silicone or the like and the external layer is made of nylon or the like. Since the bare optical fibers and the covering layer are closely adhered, the bare optical fibers and the covering layer rarely deviate to each other in an axial direction, in other words, exfoliation from one another in the axial direction rarely occurs even when external forces act on the bare optical fibers and the covering layer in opposite axial directions. However, if an excessive external force acts on them, the bare optical fibers may deviate from the covering layer. The covering part of the optical fiber is fixed to the housing with the bonding agent. But if the fixing force by close adhesion of the covering part to the bare optical fibers is smaller than the fixing force caused by bonding of the covering part to the housing, fixture between the waveguide board and the connectors can be protected from the external force. On the contrary, when the fixing force by close adhesion of the covering part to the bare optical fibers is small, it is effective to fix not only the covering part but also the bare optical fibers to the housing with the bonding agent. In general, a fixing force between the bare optical fibers and the bonding agent is larger than that between the covering part and the bonding agent. Table 1 shows three types of bonding agents A, B and C and a bonding force between the optical fibers and the optical fiber covering part. Bonding agent A is 3052C manufactured by THREE BOND INC., bonding agent B is 3057B manufactured by THREE BOND INC., and bonding agent C is LCR0628A manufactured by TOA GOSEI CO., LTD. Adhesion of Bonding Agents Bonding agent A Bonding agent B Bonding agent C Adhesion to the fiber covering part (kg/mm) 0.13 0.07 0.11 Adhesion to quartz optical fibers (kg/mm) 0.36 0.12 0.28 In a case of using, for example, the bonding agent A shown in Table 1, the bonding part of the housing 10 and the optical fibers 16 can withstand a tensile force of 1 kgf by setting the application length of the bonding agent between the housing 10 and the optical fibers to be 8 mm. In addition, it is preferable that the Young's modulus of the bonding agent is over 50kgf/mm 2 to prevent an excessive stress from being applied to the coupling part of the optical waveguide substrate 14 and the connectors 15. Fig. 3 shows a first embodiment of the present invention. In this embodiment, the covering member of the optical fiber 11 or the tape-like optical fiber cable 12 is partly removed in the first fixing portion 21. According to the first embodiment, both the bare optical fiber part 22 and the covering member part 23 are connected with the bonding agent 20 and therefore even when an external force is applied to the bare optical fibers 16 and the covering member is separated from the bare optical fibers 16 in the covering part including the optical fiber 11 and the optical fiber tape 12 therein, the external force does not act on the coupling part of the connector 15 by which the bare optical fibers 16 are held and the optical waveguide 14 in the housing 10. In the embodiment, in most cases, the adhesion of the bonding agent for quartz glass which is a material of the bare optical fibers is larger than that for nylon which is a material of the optical fiber covering member and therefore the optical fibers can be more firmly coupled to the housing 10. In addition, the optical waveguide module can be made compact by reducing the length of the first fixing portion 21. In a case of using, for example, the bonding agent A shown in Table 1, the above-described coupling part can withstand a tensile force of 1 kgf if a length along which the bonding agent is applied is set to approximately 2.2mm by removing the optical fiber covering member as much as 2mm. Fig. 4 shows a second embodiment. In this embodiment, the optical fiber covering member is partly removed from the end parts of the optical fiber conductor 11 and the optical fiber tape 12 to expose the bare optical fiber part 22, and the bare optical fiber part 22 and the covering part 23 at both ends of the bare optical fiber part 22 are fixed to the housing 10 with the bonding agent 20. According to the second embodiment, as the first embodiment, even though an external force is applied to the bare optical fibers 16 and exfoliation occurs between the bare optical fibers 16 and the covering member in the optical fiber 11 and the tape-like optical fiber cable 12, the external force does not act on the coupling part of the connector 15, which holds the bare optical fibers 16, and the optical waveguide substrate 14 in the housing 10 and therefore the bare optical fibers 16 will not be broken. Fig. 5 shows a third embodiment. In the third embodiment, there is shown an example of the first fixing portion 24 provided in the housing 10. A support block 25 is provided in the housing 10 and the waveguide substrate 14 is mounted at the center of the upper surface of this support block 25. Two connectors 15 are arranged at both sides of the waveguide board 14 and fixed to both end faces of the waveguide board 14 with the bonding agent to form the second fixing part 29. The left side connector 15 shown in Fig. 5 has a construction as shown in Fig. 6. Specifically, the optical fiber 11 is guided onto the upper surface of the silicon chip 26, the bare optical fibers 16 are fitted into a V groove 27 formed at the front end face of this silicon chip, and a holding plate 28 is bonded to the upper surface of the silicon chip. The right side connector 15 shown in Fig. 5 has a construction similar to that of the left side connector 15 and the bare optical fibers 16 of the optical fiber conductor 12 are respectively fitted into a plurality of V grooves. Both end parts of the support block 25 respectively serve as a rise part 30. The optical fiber conductor 11, the bare optical fiber part 22 from which the cover of the tape-like optical fiber cable 12 is partly removed, and the covering parts 23 located at both ends of this bare optical fiber part 22 are mounted on the upper surface of each rise part 30, and the outside of this assembly is covered with the bonding agent 20 to form the first fixing part 24. The optical fiber conductor 11 and the tape-like optical fiber cable 12 are guided out through the side wall 18 of the housing 10. In this third embodiment, the bonding strength in the first fixing part 24 is larger than that of the second fixing part 29 formed in the bonding between the waveguide board 14 and the connector 15. According to the third embodiment as other embodiments, even though an external force is applied to the bare optical fibers 16 and exfoliation occurs between the bare optical fibers 16 and the covering member 23 in the optical fiber conductor 11 and the optical fiber tape 12, the external force does not act on the coupling part of the connector 15, which fixes the bare optical fibers 16, and the optical waveguide board 14 and therefore the second fixing part 29 will not be broken. In the third embodiment, the support block 25 is independent of the housing 10 to facilitate assembly work of the optical waveguide module. Accordingly, the support block 25 can be fixed to the housing 10. Since the present invention relates to the construction for installation of the optical waveguide module, the optical waveguide is not limited to quartz-based materials and can be made of materials for semiconductors and heavy-duty dielectric materials. In addition, the connector 15 serving at the second fixing portion can be made as a chip made from various types of materials such as glass, in addition to a silicon chip. Materials for forming the housing 10 and the second holding parts 21 and 24 can be aluminum, SUS, plastics or the like, which satisfies environmental requirements for the optical waveguide module. In the case of the optical waveguide module according to the above-described embodiments, even if an external mechanical tensile force acts on optical fibers, this external force does not affect the coupling part of the optical waveguide and the optical fibers housed in the housing since the bonding strength at the fixing part of the housing and the optical fibers is determined to be larger than the bonding strength at the coupling part of the optical waveguide and the optical fibers. Therefore, the coupling part can be made to be free from damage, breakage and axial deviation, and the optical waveguide module according to the present invention can effectively apply to optical waveguide module packages to be applied in optical fiber communications services. The optical waveguide module according to the present invention is described below in more detail. As shown in Figs. 7 and 8, the housing 10 made of aluminum is a long box one end of which is provided with a tubular guide part 101 in which a circular hole is formed as a through hole and the other end of which is provided with a tubular guide part 102 in which a flat hole is formed also as a through hole. A single-optical fiber conductor 11 is passed through a circular hole of a guide-out part 101 and fixed thereto with a bonding agent 201, and a multi-core optical fiber tape 12 is passed through a flat hole of a guide-out part 102 and fixed thereto with a bonding agent 202. In this case, the bonding agents 201 and 202 to be used are preferably such that the ratio of water absorption is small, shrinkage due to hardening is less and a coefficient of thermal expansion is also small and, more particularly, the bonding agents are of a thermosetting type which can be hardened at a low temperature within a short period of time. The thermosetting type bonding agent is suitable for its high bonding force; for example, STAYCAST 2057 manufactured by GRACE JAPAN CO., LTD and EPO-TEC 302-3 manufactured by RIKEI CO., LTD can be used. Bonding with the bonding agents 201 and 202 can be done only on the external nylon cover or the internal cover such as silicone resin, or both covers can be bonded to the through holes of the guide-out parts 101 and 102. According to the invention the bonding strength is increased by bonding these covers and the bare optical fibers simultaneously to the through holes, respectively. The waveguide board 14 is housed in the housing 10 and bonded in advance to the connector 15 which fixes optical fibers (bare optical fibers). The connector 15 comprises a silicon chip provided with V grooves and a holding plate and is bonded to hold bare optical fibers therein. In this case, a bonding agent with less shrinkage caused due to hardening and a small coefficient of thermal expansion is selected for bonding the connector 15 and the waveguide substrate 14 at their end faces. A bonding agent which is hardened either by irradiation of an ultraviolet ray or by heating is preferable. Bonding of the waveguide board 14 and the connector 15 can be implemented more completely by temporarily fixing the waveguide substrate 14 and the connector 15 with irradiation of the ultraviolet ray, then fixing optical fibers 11 and 12 to the housing 10 with a thermosetting type bonding agent. Moreover, the refractive index N 1 of the bonding agent for fixing the waveguide board 14 and the connector 15 is preferably as given below, where the refractive index of the optical waveguide is N 0 and the refractive index of the core of optical fiber is N 2 : N 1 = (N 0 · N 2 ) 1/2 This is for reducing the loss of transmitting light at the bonded part. In view of the above, the following bonding agents are used to fix the waveguide board 14 and the connector 15; for example, an ultraviolet hardening type bonding agent UV-2100 manufactured by DAIKIN KOGYO CO., LTD., an ultraviolet hardening type bonding agent LCR0277 manufactured by TOA GOSEI CO., LTD. and LCR10026/65A to which a UV catalyst and a heat catalyst are added are used. As shown in Figs. 7 and 8, the module unit is built in the housing 10 and the internal chamber is sealed by a cover 300. This cover 300 can be fixed by welding or by a bonding agent. An inactive gas such as nitrogen is sealed in the housing 10. In this case, though the waveguide board 14 can be bonded to the bottom of the housing 10, these parts are bonded only at their partial surfaces and not at their full surfaces. If the overall surfaces of these parts are bonded, exfoliation is prone to occur due to thermal shrinkage. In the embodiment shown in Figs. 9 and 10, the housing 10 and the cover 300 are made of polycarbonate. The guide-out parts 101 and 102 for holding optical fibers are respectively composed of lower parts 101A and 102A which are integrated with the housing 10 and separate upper parts 101B and 102B. In this embodiment, the external and internal covering members at the end parts of the optical fiber conductors 11 and 12 are removed to expose bare optical fibers. The end parts of bare optical fibers are held by the connector 15 and treated with a bonding agent, and the end faces are ground. After this, the connector 15 is bonded to both end faces of the waveguide board 14 and this assembly is set in the housing 10. Then the upper parts 101B and 102B of the guide-out parts 101 and 102 are set and the optical fiber conductor is fixed with the bonding agent. The housing 10 is filled with an inactive gas. Thus the optical waveguide module is completed. From the invention thus described, it will be obvious that the invention may be varied in many ways within the scope of the following claims.

Claims: An optical waveguide module comprising: a module unit including: a waveguide substrate (14) on which an optical waveguide (13) is formed; and a fiber connector (15) fixed on the waveguide substrate (14) and holding an end of an optical fiber (11; 12) which comprises a bare optical fiber (16) and a coating (23) covering same; a housing (10) accommodating the module unit and having a guide part (18; 19; 101; 102) through which the optical fiber (11; 12) is led to the exterior of the housing (10), the optical fiber (11; 12) being fixed to the housing (10) at the guide part (18; 19; 101; 102); a first bonding agent (20; 201; 202) for fixing the optical fiber (11; 12) to the housing (10) to thereby form a first fixing portion (21) between the optical fiber (11; 12) and the housing (10); a second bonding agent for fixing an end surface of the waveguide substrate (14) to an end surface of the fiber connector (15) to thereby form a second fixing portion (17) between the end surface of the fiber connector (15) and the waveguide substrate (14); wherein the fixing strength between the optical fiber (11; 12) and the housing in the first fixing portion (21) is greater than the fixing strength between the waveguide substrate (14) and the fiber connector (15) in the second fixing portion (17); and a part of the coating (23) is removed from the optical fiber (11; 12) to expose a portion of the bare optical fiber (16), and the first fixing portion (21) is formed by fixing both at least part of the exposed portion of the bare optical fiber (16) and an adjacent portion of the coating (23) to the housing (10) with the first bonding agent (20; 201; 202). An optical waveguide module according to claim 1, wherein the optical fiber (11; 12) has a bare optical fiber portion (22) and two coating portions (23) spaced apart from each other and connected by the bare optical fiber portion (22), and the first fixing portion (21) is formed by fixing both coating portions (23) and the bare optical fiber portion (22) therebetween to the housing (10) with the first bonding agent (20; 201; 202). An optical waveguide module comprising: a module unit including: a waveguide substrate (14) on which an optical waveguide (13) is formed; and a fiber connector (15) fixed on the waveguide substrate (14) and holding an end of an optical fiber (11; 12) which comprises a bar optical fiber (16) and a coating (23) covering same; a housing (10) accommodating the module unit and having a guide part (18; 19; 101; 102) through which the optical fiber (11; 12) is led to the exterior of the housing (10); a support block (25) for mounting the module unit and accommodated in the housing (10), the optical fiber (11; 12) being fixed to an end portion (30) of the support block (25) ; a first bonding agent (20) for fixing the optical fiber (22; 23) to the support block (25) to thereby form a first fixing portion (24) between the optical fiber (11; 12) and the support block (25) ; a second bonding agent for fixing an end surface of the waveguide substrate (14) to an end surface of the fiber connector (15) to thereby form a second fixing portion (29) between the end surface of the fiber connector (15) and the waveguide substrate (14); wherein the fixing strength between the optical fiber (11; 12) and the support block (25) in the first fixing portion (24) is greater than the fixing strength between the waveguide substrate (14) and the fiber connector (15) in the second fixing portion (29); and a part of the coating (23) is removed from the optical fiber (11; 12) to expose a portion of the bare optical fiber (212), and the first fixing portion (24) is formed by fixing both at least part of the exposed portion of the bare optical fiber (22) and an adjacent portion of the coating (23) to the support block (25) with the first bonding agent (20). An optical waveguide module according to claim 3, wherein the optical fiber (11; 12) has a bare optical fiber portion (22) and two coating portions (23) spaced apart from each other and connected by the bare optical fiber portion (22), and the first fixing portion (21) is formed by fixing both coating portions (23) and the bare optical fiber portion (22) therebetween to the support block (25) with the first bonding agent (20). An optical waveguide module according to any one of claims 3 to 4, wherein the support block (25) is fixed to the housing (10). An optical waveguide module according to any one of the preceding claims, wherein the optical fiber (12) is a tape type optical fiber including a plurality of bare optical fibers (22) arrayed in parallel and covered by the coating (23). An optical waveguide module according to any one of the preceding claims, wherein the fiber connector (15) has a substrate (26) on which one or more grooves (27) are provided, each with a V-shaped section for holding the optical fiber (11; 12). An optical waveguide module according to any one of the preceding claims, wherein the guide portion (18; 19; 101; 102) comprises a wall (18) of the housing (10) having an aperture therethrough which the optical fiber (11; 12) passes. An optical waveguide module according to any one of the preceding claims, wherein the housing (10) further comprises a cover (300) for closing an opening to an internal space of the housing (10) in which the module unit is accommodated, the cover (300) being fixed to the housing (10) to seal the internal space. An optical waveguide module according to claim 9, wherein the sealed internal space is filled with an inactive gas. An optical waveguide module according to any one of the preceding claims, wherein the second bonding agent is an ultraviolet ray hardening type agent or a thermosetting type agent, and the first bonding agent (20; 201; 202) is a thermosetting type agent.

Inventors: ISHIKAWA SHINJI, SEMURA SHIGERU, SUGANUMA HIROSHI, YUI DAI, ISHIKAWA, SHINJI, SEMURA, SHIGERU, SUGANUMA, HIROSHI, YUI, DAI, ISHIKAWA, SHINJI, C/O YOKOHAMA WORKS OF, SEMURA, SHIGERU, C/O YOKOHAMA WORKS OF, SUGANUMA, HIROSHI, C/O YOKOHAMA WORKS OF, YUI, DAI, C/O YOKOHAMA WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1994
Main classification: G02B6
IPC codes: G02B6